ipv6: add daddr/final storage in struct ipv6_pinfo

After commit b409a7f ("ipv6: colocate inet6_cork in
inet_cork_full") we have room in ipv6_pinfo to hold daddr/final
in case they need to be populated in fl6_update_dst() calls.

This will allow stack canary removal in IPv6 tx fast paths.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260206173426.1638518-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

include/linux/ipv6.h

@@ -230,6 +230,10 @@ struct ipv6_fl_socklist;
 struct ipv6_pinfo {
 	/* Used in tx path (inet6_csk_route_socket(), ip6_xmit()) */
 	struct in6_addr 	saddr;
+	union {
+		struct in6_addr daddr;
+		struct in6_addr final;
+	};
 	__be32			flow_label;
 	u32			dst_cookie;
 	struct ipv6_txoptions __rcu	*opt;